Funds are requested for the purchase of a high-throughput matrix-assisted laser desorption/ionization (MALDI) mass spectrometer. This instrument will be primarily configured for and dedicated to the acquisition of SUPREX data. SUPREX (Stability of Unpurified Proteins from Rates of H/D Exchange) is a new H/D exchange- and MALDI-based method for measuring the thermodynamic stability of proteins in solution. The SUPREX techique was born out of a collaboration between the Fitzgerald and Oas laboratories at Duke University five years ago. Over the past five years the SUPREX technique has been developed into a robust analytical method for the quantitative thermodynamic analysis of proteins and protein-ligand complexes. A total of 14 published works on the SUPREX analysis of selected model protein systems have served to define the accuracy, precision, and generality of the technique. [unreadable] [unreadable] With the experimental protocols and data analysis methods of SUPREX firmly established, the bottleneck in the generation and analysis of SUPREX data has become the acquisition of MALDI mass spectra. Approximately 500 mass spectra are required for the complete SUPREX analysis a protein or protein-ligand system; and the use of SUPREX in combinatorial chemistry applications can require the acquisition of millions of MALDI mass spectra. The high-throughput capacity of the requested MALDI mass spectrometer system is essential for the Co-PI's on this proposal to exploit the unique advantages of SUPREX (e.g. the ability to rapidly analyze just pmol quantities of protein in both purified and unpurifed form) in their NIH-funded projects that require such thermodynamic measurements on proteins and protein-ligand complexes. The increasing number of SUPREX users on the Duke campus and the proposed exploitation of SUPREX in combinatorial library screening projects create a critical need for a new high-throughput MALDI-TOF mass spectrometer dedicated to SUPREX experiments on the Duke campus. [unreadable] [unreadable]